Transmission line



May 7, 1935. N. E LINDENBLAD 2,000,032

TRANSMISSION LINE Filed June 25, 1933 5 OUTPUT cmcu/r H/GH rfisauzwr IINPUTC/RCU/T t 2 I INVENTOR NILS E. LINDEN BLAD ATTORNEY Patented May 7,1935 more TRANSMISSION LINE Nils E. Lindenblad, Port Jefierson, N. Y.,assignor to Radio Corporation of America, a corporation of DelawareApplication June 25, 1930, Serial No. 463,610

13 Claims.

This invention relates to transmission lines and has as its prime objectthe provision of a new and useful'method and means for insulating-high hfrequency transmission lines from their supports and for couplingtogether a plurality'oftransmission lines.

- Much diificulty has been encountered in supporting transmission linesused in transmitter -work, for example, wherein high frequency highvoltage alternating currents are encountered. In order to preventradiation from the transmission lines, it is desirable that they be kepttogether as close" as possible since, with lines of oppositeinstantaneous polarity, there is mutual radiation cancellation. THowever, to keep the lines close together and yet at their supportingpoints to keep them properly insulated from the supports was heretoforeimpossible of accomplishment for the reason that, due to the highvoltages involved, the insulators had to 'be of extremely large size.Hence, at the supporting points at least the transmission lines had todiverge.

' The foregoing difliculty is overcome by the "present invention whichhas, as a further object, the-utilizationin the support and connectionof -transmission lines,'oftheprinciple that a U- shaped path one-halfwave length long offers very high-impedance to electrical energy whosefrequency corresponds to the frequency for which the pathisone-halfwave-length long. This object is carried out by connecting or couplingacross .the transmission lineat points where it is to be supported apath of low impedanceto-radio frequency currents, preferably a deadshort circuit, and this "short circuiting connection-is directlyconnected by means of supporting cables or the liketo a support.Coupling to another transmission line is accomplished by tapping on tothe transmission line theline .tobe coupled thereto at one-quarter wavelength or less away from the short circuiting connection.

[As the short circuiting connection is at a voltage nodarpoint by virtueof the reflections set up thereby, it may be safely grounded or,in other'45 wordsnconnected to a support without danger and without loss ofpower. As the coupled lines are connected together at points one quarterwavelengthaway from the short circuiting connection, the portions of theshort circuited line betweenthe short circuit and the tapping points issubstantially one-half wave length long, substantially U -shaped, andhence, ofiers substan- ;t ially infinite impedance to energy transferredby either of the lines so connected together.

" In the event that a transmission line is to be of the presentinvention.

supported intermediate its. ends, it is a further object of thisinvention to provide a path paral-' leling the transmission line at thepointat which it is to be supported which path is substantially one-halfwave length long and which may, there:-

5 fore, be safely connected to a"supportiby even conductive cables orthe like at its voltagenodal point} Here also, the reason why thismayribe done is'the fact that the path offers substantiallyinfiniteimpedance to energy transferred by :the line which it supports.a 3

The invention may further be understood by referring to the accompanyingdrawing wherein 3 Figure l is illustrative of the presentinvention,showing terminal and intermediate supports for a transmission linecoupled to other transmission lines, I

Figure 2'discloses the present invention applied to a bent transmissionline supported at the bendingpoint, I 20 Figure 3 is a detailed view inelevation of a short circuiting connection used, for example, in Figures1 and 2, and

Figures 4 and 5 are given by way of explanation .25 Turning to Figure 1a high frequency inputcircuit 2 supplies energyov'er' transmission lines4, 6 and. 8 to an output circuit In; a i Ordinarily, as'transmissionline 6 is mounted some distance above the ground and is fairly long itmust be, as indicated, supported at its ends and intermediate its ends.To support linet at its ends A; B, by means of ordinary insulators wouldinvolve spreading of the lines, undue radiation, and large losses. Toovercome these objections, paths of low impedance to the high frequencycurrent transmitted by the line 6; namely, short-circuiting straps I2are connected directly across the line 6 at its terminal supportingpoints A, B. The straps may be bolted together bysuitable bolts M ofsuitable number. At end A'the two wires forming the transmission line 6may be brought together at point it, passed over a pulley l8 mountedonsupport 2G and pulled taut by weight 22. At point B the wires formingtransmission line 6 may be fastened in any suitable fashion to a support24. o

Transmission line 4 coupling-the input circuit 2 to transmission line 6is connected or tapped adjustably at points 26, 28 to transmission-line6 symmetrically and one-quarter wave length away .po'itlng elements of-a weight 54. -means of an intermediate line 56 adjustably tap- Byvirtue of the foregoing connection, and be- .cause of the fact thatstrap I 2 is of negligible length relative to the portion oftransmission line 6 included between adjustable tapping points 26, 28and strap l2, strap I2 is at a voltage nodal point and may be safelyfastened without energy loss to a support. In other words, the supply tothe transmission line 6 is through line 4 to points 26, 28 which lookingtowards point A face into an effective infinite impedance by virtue ofthe fact that the U-shaped portion of the line formed by the strap l2and the portion of the line 6 included between it and points 25, 28 actsas a tuned circuit. V Y

The tapping of points 26, 28 to the line 6 is not critical but may besomewhat more or less than one-quarter wave length away from shortclrcuiting strap l2. Even with the lessened or increased distance theportion of the line between the tapping points and the support oifers anexceptionally high impedance as indicated by the graph forming Figure.It is not until the tapping points are brought very close to the strapI! or a half way position that impedance, is reduced to' such an extentthat it becomes dangerousto directly support-the line by metallicelements to a grounded support.

In anotheraspect, it may be said that by tapping the lines 4 and 8 tothe transmission line 0 .inthe manner described, a U-shaped circuit iseffectively connected thereacross as shown in Figure 5.- Point 30 whenthe. U-shaped element 32 is properly slid along the tapping points 26,28

, would be at zero potential and could be supported by any metallicsupporting element 34. Point 30 would correspond to the strap l2 ofFigure l and element 34 to the supporting cables and sup- Figure l forthetransmission line 6.

To support the line 6 of Figure 1 intermediate it's ends, it is onlynecessary, in the light of the invention so far described, to provide ahalf-wave length path paralleling the transmission line intermediate itsends and'fastened at its voltage nodal point to a support. In Figure 1elements 36, 38 are each approximately one-quarter wave length long andextend from line 6 to short circuiting strap 40 and form with this strapa path U=shaped and one-half wave length or less long parallelingtransmission line 6 and, as at points A and B, this pathor looped,U-shaped connec- "tion may be-fasten'ed to any suitable support 42.

If desired, an additional U-shaped support extending from the line 6 maybe placed on the other side of the line 6 asat 44.

The application of the present'invention to a bent transmission line isshown in Figure 2.

Energy may be considered as traveling from point C to point D. The lineC is short circuited by means ofstrap 46 and the line D by a strap 48.The wires forming the lines may be brought .together at 50, wound abouta pulley fastened to asupport at 52 and counterweighted by means of Thelines arejoined together by pedto the lines C and D at points 58, 60, 62and 64 at points not over one-quarter wave length away from the shortcircuiting straps 46, 48.

Having thus described my invention, what I claim is:

1. In combination, in high frequency apparatus, an input circuit, anoutput circuit, a transmission line for transferring energy from theinput circuit to the output circuit, means at the terminal ends of theline having low impedance to high frequency energy, and connectionsbetween the input and output circuits and the line, these connectionsbeing coupled to points on the line each approximately one-quarter wavelength away from said last mentioned means.

2. The combination, in high frequency apparatus, of an input circuit, anoutput circuit, a transmission line for transferring energy from theinput circuit to the output circuit, short circuiting connectionsterminating the line, and connections between the input and outputcircuits and the line, these connections being coupled to the lineapproximately one-quarter wave length away from the short circuitingconnections.

3, The combination as claimed in claim 1 having in additionmeans havingan overall length of approximately one-half wave length or lessparalleling the line intermediate its ends and fastened at its voltagenodal point to a support.

4. The combination as claimed in claim 2 having in addition a loopedconductor having an overall length of approximately an odd multiple ofone-half wave length paralleling the transmission line and connectedthereto intermediate its ends, said looped conductor being fastened to.a support substantially at its voltage nodal point.

5. In a transmission system wherein high 'frequency high voltagealternating currents are utilized, a two wire transmission lineterminating in a loop, said loop being approximately one-half wavelength long at the fundamental frequency and offering very highimpedance to electricalenergy in said transmission line of thefundamental frequency, and high frequency apparatus connected acrosssaid transmission line at the terminals of said loop.

6. A high frequency system utilizing high voltage alternating currentshaving, in combination, a two wire transmission line, a metallic strapcomprising a path of .low impedance to radio frequency currents acrosssaid line, an input circuit, and means from said input circuit topointson said two wire line which are substantially symmetrically placed withrespect to. said pathand separated from each other approximately an saidline and path.

7. In combination, a short circuited two wire transmission line, asecond short circuited two wire transmission line, and connectionsbetween said two lines extending from points on one of said lines, eachpointbeing approximately onequarter wavelength away from the shortcircuit thereof to points on the other line also each approximatelyone-quarter wave length away from the other short circuit. I

8. A high frequency system utilizing high voltage alternating currentshaving, in combination, a two wire transmission line, a metallic strapcomprising a path of low, impedance to radio frequency currents acrosssaid line, an input circuit, and connections from said input circuit topoints on said two wire line which are each substantially symmetricallyplaced with respect to said path and separated from each otherapproximatelyan odd multiple of a half wave length along said line andpath. g

9. In combination, a two wire transmission line supported at least atone end thereof, a short circuit connection across said transmissionline at said one end, and high frequency apparatus connected across saidtransmission line at points approximately one quarter wave length fromsaid short circuit connection, said short circuit connection beingsubstantially a voltage nodal point at which said line is supported.

10. In combination, a two wire transmission line supported at least atone end thereof, a path of low impedance to high frequency energyconnected across said transmission line at said one end, and highfrequency apparatus connected across said transmission line at pointsapproximately an odd multiple of a quarter wave length from said path oflow impedance, said path of low impedance being substantially a voltagenodal point at which said line is supported.

11. A system in accordance with claim 10 characterized in this, thatsaid transmission line is adjustable with respect to said high frequencyapparatus at said points of connection thereto.

12. In a high frequency high voltage communication system, incombination, two high frequency conducting elements, each elementcomprising a pair of collaterally spaced linear wires, connectionsjoining together the ends of the wires of each element, each connectioncomprising a U shaped loop substantially one half wave length longhaving its legs connected to the wires through substantiallynon-radiating paths, said elements being connected together at theterminals of one of said U shaped loops.

13. In combination, high frequency apparatus, a two conductortransmission line having bridged thereacross a path of low impedance todirect current, and a two wire connection extending from said highfrequency apparatus to said line, each wire of said connection beingcoupled to a point on one of said conductors of said transmission line,the overall distance between said coupling points as measuredon said twoconductor transmission linethrough said path of low impedance beingapproximately an odd multiple of a one-half wave length.

NILS E. LINDENBLAD.

